Light up UpdatePod (#613)

* Light up UpdatePod

This PR updates the vkublet/pod.go createOrUpdate(..) method to actually handle
updates. It gets the pod from the provider as before, but now if it exists the method
checks the hash of the spec against the spec of the new pod. If they've changed, it
calls UpdatePod(..).

Also makes a small change to the Server struct to swap from kuberentes.Clientset to kubernetes.Interface
to better facilitate testing with fake ClientSet.

Co-Authored-By: Brian Goff <cpuguy83@gmail.com>

vkubelet/vkubelet.go

@@ -22,7 +22,7 @@ const (
 type Server struct {
 	namespace       string
 	nodeName        string
-	k8sClient       *kubernetes.Clientset
+	k8sClient       kubernetes.Interface
 	provider        providers.Provider
 	resourceManager *manager.ResourceManager
 	podSyncWorkers  int